This invention relates to an automatic strapping machine which feeds strap automatically around an article or a package, tensions the fed strap, and secures overlapped strap ends in place by a joint or seal. When thermoplastic strap is used, the joint is formed by frictionally fusing together the interface regions of overlapped strap portions.
It is known to tie packages of various shapes and configurations by means of thermoplastic strap. While such strap can be secured in place using an external seal which is crimped about overlapping strap regions or by the so-called hot knife method, in many instances it is more desirable to secure the strap by fusing together the overlapping strap ends by the generation of heat in situ by the rapid relative movement of overlapping strap portions which are biased toward one another by externally applied pressure. Joints formed in the foregoing manner are commonly referred to as friction-fused joints.
Various tools have been employed for forming a frictionfused joint; however, such tools usually place both overlapped strap portions in tension during joint formation. One such tool is disclosed in U.S. Pat. No. 3,442,203 to Kobiella. While a highly efficient joint can be formed in this manner, the tensioned strap portions tend to dampen the oscillatory motion of the sealing energy generating means and require a relatively high initial energy input. Other friction-fusion sealing tools are shown in U.S. Pat. No. 3,442,733 and U.S. Pat. No. 3,654,033.
Moreover, in many packaging applications it is desirable to feed strap at a relativly high rate about a package and to pull considerable tension on the strap that has been looped about a package, yet any increase in tension further dampens the oscillations needed to produce a friction-fused joint. Also, convenient means for the rapid feeding of strap about a package and the pulling of relatively high tension in the strap looped about a package heretofore have not been available.